Many industrial and research projects require that certain procedures be performed in a so-called "clean room " environment. The objective here is to eliminate all dust particles that might carry contamination with them, or themselves interfere with the operation of delicate instruments. Essentially, a "clean room" is merely a room equipped with a highly effective filtration system. It has become standard practice to design these filter installations so that the ceiling area of the room is occupied by a large number of filtration modules that are fed from a common duct or plenum. Air is delivered into the room via the system, and withdrawn through a conventional exhaust outlet adjacent the floor. This type of installation is sufficiently common to have generated a relatively standard form of replaceable filter element. These are rectangular in configuration, and usually have an edge frame provided with a sealing gasket that can be pressed against an abutment surface on the module housing to generate a sufficiently tight seal to assure that all of the air entering the room passes through the filter, rather than around it.
The filter elements must be replaced frequently as they become loaded with entrapped materials. The module structures in most common use at present are adapted for the installation of the filter elements from above, so that they are dropped into position and held down against a retaining flange defining an opening through which the air through the filter enters into the room. This arrangement presents a problem, in that the access to the filter modules from above is very inconvenient, with the alternative being the removal of the entire module so that access to the top can be obtained. Whenever ducting is connected and disconnected, or disturbed by jostling, there is an increased risk of contaminating the air of the room during the filter-changing process. If this occurs, the filtration equipment must necessarily be run for a long enough period to purge the room before the room can be used for its special purpose. The time factor involved in such a replacement procedure is obviously very substantial, and blocks the use of the room during this period.